Differential Expression of Leucocyte Protein L1 (Calprotectin) By Monocytes and Intestinal Macrophages

Abstract

LI is a major cytosol protein complex present in virtually all circulating monocytes and neutrophilic granulocytes¹, but expressed by only a subset of tissue macrophages.² It consists of two subunits (L1_L and L1_H chains) which are identical to the proteins called MRP-8 and MRP-14.³ Its abundant occurrence in vivo as heterodimers (and perhaps tetramers) in neutrophils and monocytes has recently been confirmed. ^4,5 The cDNA sequence of MRP-8 was reported to be nearly identical to that of the cystic fibrosis antigen ^6,7 L1 has calcium-binding properties and the alternative name calprotectin reflects its antimicrobial properties 8 Antiproliferative properties against tumour cell lines have also been found.⁹ L1 has been reported to be associated with the cytoskeleton of keratinocytes^10,11 and monocytes^1,2 in a calcium-dependent manner; this could possibly be of importance for motility and recruitment of the latter cells. Thus, the abundant expression of this protein by inflammatory leucocytes, including reactive macrophages, ² is supposedly of significant biological importance in local defence.